Sertoli cell cultures of rats and mice will be used to study the transduction of hormonal signals as related to the cyclic nucleotide metabolism. We propose to: 1. Determine the proliferating and differentiating ability of Sertoli cells in primary cultures, the feasibility of serial cell transfers without loss of differentiation, and the possibility of establishing Sertoli cell cultures of aging animals to follow the course of hormone-dependent cyclic nucleotide changes. 2. The biochemical characterization of cAMP-dependent protein kinase activity and the immunocytochemical localization of the holoenzyme and its subunits (Ri, R2, and C). 3. The effect of hormones, serum and other growth factors on the subcellular localization and activity of adenylate and guanylate cyclase. 4. Transmission and scanning electron microscopic studies of hormonally induced cell shape changes. 5. The study of Sertoli cell-germinal cell interaction in vitro in relation to hormonally induced metabolic changes in Sertoli cells. Results of these studies may be relevant for understanding the cell biology of Sertoli cell coordinated by signals triggered by ligands and chemical messengers as well as to provide information on the relationship of somatic cell activity (Sertoli cell) and germinal cell differentiation in the male.